Five section full powered telescopic crane boom

ABSTRACT

A five section telescopic crane boom is extended and retracted by a pair of three section hydraulic rams which are fully enclosed by the boom and independently suspended therein. The suspension means for the rams compensates for cocking and bending of the boom sections when the latter are extended under load and relieves the rams of bending stresses and allows them to remain substantially straight, thus preventing leakage of the ram operating fluid.

United States Patent 1191 Sung 1 1 Feb. 19, 1974 1 FIVE SECTION FULLPOWERED 3,353,686 11/1967 Cowan 212 55 O IC CRANE O 3,398,492 8/1968Nansel 52/115 3,212,604 10/1965 Garnett 212/55 lnvemori Fu-Tlen g,waynesboro, 3,398,645 8/1968 Nansel 52 115 [73] Assignee: Kidde Walter &Company, Inc.,

Clifton, NJ. Primary Examiner-Henry C. Sutherland AssistantExaminer-Les1ie K. Braun [22] 1971 Attorney, Agent, or Firm--Brady,OBoyle & Gates [21] Appl. No.: 132,407

. [57] ABSTRACT 2% 8 52/115 52/ 53 A five section telescopic crane boomis extended and d retracted by a pair of three section hydraulic rams 1o earc which are fully enclosed by the boom and independently suspendedtherein. The suspension means for the rams compensates for cocking andbending of the [56] ,References Clted boom sections when the latter areextended under UNITED STATES PATENTS load and relieves the rams ofbending stresses and al- 3,722,154 3/1973 Sakamoto et a1. 52/121 lowsthem to remain substantially straight, thus pre- 3,624,979 12/ 1971Przybylski 52/115 venting leakage of the ram operating fluid. 3,445,004I 5/1969 Grider et a1. 212/55 1 3,243,052 3/1966 Grove 212/55 16 Claims,16 Drawing Figures PATENTEDFEBI 9mm" SHEET 1 [If 4 FIG. l5

INVE NTOR FU-TIEN SUNG ATTORNEYS PATENTEU FEB 1 9 I974 SHEET 2 0F 4SHEET 3 OF 4 PATENIE FEB 1 9 I874 FIVE SECTION FULL POWERED TELESCOPICCRANE BOOM BACKGROUND OF THE INVENTION are now quitecommon but generallyspeaking booms of greater length having more than four sections have notbeen practical to construct for a number of reasons. Among these reasonsis the inability to mount the required number of operating rams insideof the hollow telescopic boom without increasing the cross sectionalsize of the boom beyond reasonable limits. Additionally, where attemptshave been made to employ a smaller number of rams containing more thanthe customary two sections, a serious leakage problem is encounteredwhen the boom is extended. A significant degree of cocking necessarilyoccurs between the extended boom sections plus some bending of thesesections under loading. This cocking and bending is transmitted to theplural section rams when they are rigidly connected with the boomsections, causing them to flex or bend, giving rise to the seriousleakage of fluid. At least one prior art effort has been made to providea five section telescopic boom in which the internal hydraulicallyoperated rams are interconnected so as to be mutually self-supporting,as in US. Pat. No. 3,21 2,604 to Garnett. However, in this prior artstructure, when the boom is extended andthe rams are under heavyloading, they are subjected to very severe bending stresses and theabove leakage problem is necessarily present. v

Theobjective of the present invention is, therefore, to provide anentirely practical and economically feasible five section telescopiccrane boom in which the operating rains for the boom are fully enclosedand independently supported in sucha manner that the inherent cockingand flexure of the extended boom is nottransmitted to 'the'rams as asevere bending stress, and consequently the rams are able to remainsubstantially straight atall times and the problem of severe leakage islargely avoided. In the invention, it has been found feasible to employa single pair of double telescoping rams, each ram having threesections, and the rams being fully enclosed within the five sectionboom. All sections of the telescopic boom are fully powered by havingeach extensible section of each ram connected with one extensible boomsection. The suspension or mounting means for the rams is such that acertain degree of relative lateral movement between the boom sectionsand rams may occur to relieve the rams of bending stresses during theinevitable cocking and bending of the bo'om'sections when the boom isextendedfThe inventionpossesses other unique features and advantageswhich appear during the course of the following description.

BRIEF DESCRIPTION OF DRAWING FIGURES ,embodying the subject matter ofthe invention.

FIG. 2 is a diagrammatic side elevation of the boom and its operatingrams fully extended.

FIG. 3A is a fragmentary longitudinal vertical section on an enlargedscale showing that portion of the boom designated FIG. 3A in FIG. 2.

FIG. 3B is a similar view showing that portion of the boom designatedFIG. 3B in FIG. 2. 7

FIG. 4 is a longitudinal vertical section through the boom when the-sameis fully retracted.

FIG. 5 is an enlarged fragmentary end elevation, partly in section,taken .on line 5-5 of FIG. 3B.

FIG. 6 is an enlarged transverse vertical section taken on line 6-6 ofFIG. 3B.

FIG. 7 is a fragmentary horizontal section taken on line 77 of FIG. 6. 1

FIG. 8 is a similar view taken on line 8-8 of FIG. 6

FIG. 9 is an enlarged transverse vertical section taken on line 9-9 ofFIG. 3B.

FIG. 10 is a similar view taken on line 10-10 of FIG. 3B. 1

FIG. 1 l is a similar view taken on line 1 1-1 1 of FIG. 3A.

FIG. 12 is a fragmentary horizontal section taken'on line 12-12 of FIG.11. I

FIG. 13 is an enlarged transverse vertical section taken on line 13-13of FIG. 3A.

FIG. 14 is a diagrammatic side elevational view of the extended boomshowing on an exaggerated scale the cocking and bending of the boomsections and also-illustrating the relative straightness of the extendedrams.

FIG. 15 is a fragmentary perspective view of a modified mounting meansfor a ram.

DETAILED DESCRIPTION Referring to the drawings in detail wherein likenumerals designate like parts throughout the same, a crane boom shown inits entirety at 20 comprises a base section 21, first, second and thirdmid-sections 22, 23 and 24 and a fly section 25, all telescopicallyinterfitting. As shown in FIG. 6, each boom section is rectangular incross section and fabricated from welded plate stock as disclosed inprior copending application Ser. No. 200,352, now-Pat. No. 3,690,742,issued Sept. 12, 1972, a continuation of Ser. No. 90,373, filed Nov; 17,1970, for CRANE BOOM now abandoned. This fabricated construction allowsthe placementof wear pads 26 or similar bearing means substantially indirect alignment with the vertical walls of the box-like boom sections,thus greatly reducing transverse flexure of the bottom walls oftheseveral sections and permitting the use of thinner material for thesewalls. Equivalent upper bearing means 27in the form of rollers or wearpads is also provided between-the adjacent telescoping boom sections.

The means to extend and retract the telescopic boom consisting of thefive boom sections comprises a pair of double-acting,double-telescoping, three section bydraulic rams 28 and 29 arrangedtotally inside of the hollow boom and each independently-supportedtherein in a manner to be fully described. The mounting or suspensionmeans for the rams 28 and 29 forms a very important part of theinvention. The inner or rearward ram 28 includes a cylinder section 30,ram mid-section 31 and a rodsection 32. The cylinder section 30 ispivotally secured at its rear end to the base section 21 of the boom bya suitable fixed pivot element 33. The cylinder section 30 extendsforwardly into the first mid-section 22 even when the crane boom isfully extended, FIG. 3A, and its forward end portion is supported by awiper ring 34 whose upper end carries an upstanding pin 35 rigidtherewith, having a head 36 on its upper end resting on the top of acompression spring 37. The bottom of this spring is seated on the bottomwall of a suspension bracket 38, dependingly rigidly secured to the topwall of the first mid-section 22 of the telescopic boom. Therefore, theforward end portion of the cylinder30 of ram 28 is resiliently suspendedfor limited vertical movement through the wiper ring 34 and theassociated spring suspension means from the rear end portion of thefirst mid-section 22. It will be understood that the wiper ring 34 andassociated parts move with the first mid-section 22 as the boom isextended or retracted and therefore the wiper ring moves outwardly andinwardly over the cylinder 30 between the positions shown in FIGS. 3A

and 4 where the boom is fully extended and fully retracted,respectively.

Adjacent the cylinder 30 and mid-section 31 of inner ram 28 is afabricated housing 39 made from welded rod stock so that the housing issimilar in construction to a certain type of truss formed of welded rodstock. The housing is channel-like and U-shaped in cross section and hasits top open. It includes corner longitudinal rods 42, whose rear endsare rigidly secured to a rear end plate 43 on the first mid-section 22of the boom. The forward ends of the rods 42 are similarly anchored to ahead plate 44 on the forward end of ram mid-section 31. Consequently,when the inner ram 28 is extended and its mid-section 31 movesforwardly, the first mid-section 22 of the..boom will be pulledforwardly by the housing 39 due to the connection of the rear end of thehousing with the plate 43.

In turn, the forward end of the housing 39 is additionally supported bya wiper bearing or suspension element 45 which is rectangular in crosssection, FIG. 11, and slidably contacts the corner rods 42 of thehousing 39, as shown. The wiper bearing 45 at its top carries anupstanding pin 46 having a rigid head 47 bearing downwardly on acompression spring 48, seated on a suspension bracket 49, dependinglyrigidly secured to the top wall of the second boom mid-section 23. Thus,the housing 39 and ram 28 are additionally resiliently supported forlimited vertical movement within the boom through the elements 45through 49, described immediately above. When the boom is extended orretracted, the wiper bearing 45 will slide over the truss-like housing39 either forwardly or rearwardly between the extreme positions depictedin FIGS. 3A and 4. In FIG. 1 1, the boom is extended and the wiperbearing 45 is near the outer end of housing 39. Due to the cantileveredattachment of the housing 39 to boom mid-section 22, its outer end isfree to move vertically and the force of spring 48 is sufficient toelevate the forward end of the housing 39 as depicted in FIG. 11. Whenthe boom is fully retracted and the wiper bearing 45 is close to therear end of the housing 39 where this housing is rigid with boommid-section 22 and cannot yield, the spring 48 will be compressed andthere will be a substantial gap between the elements 45 and 49. When theboom is extended, the wiper bearing 45 may contact the bracket 49 ormove very close thereto, FIG. 11, and in like manner the head 47 maysubstantially contact the top wall of boom mid-section 23.

Another housing 50 also constructed from rod stock and beingchannel-like or U-shaped in cross section, FIG. 10, is adapted totelescope over the housing 39. Both of these truss-like housings lendrigidity in two directions because of their deep channel configurations.The corner rods 51 of the housing 50 are anchored at their rear ends toa plate 52 at the rear end of the second mid-section 23. The forward endof the housing 50 is rigidly secured to a head plate 53 on the rodsection 32 of ram 28. Thus, when ram 28 is extended and the rod section32 moves forwardly, the housing 50 at its rear end pulls the secondmid-section 23 of the boom forwardly.

The leading end of rod section 32 carries a cross pin 54 rigid therewithhaving a lost motion connection with a pair of upstanding support plates55 through vertical slots 56 formed in the latter. The plates 55 havetheir lower ends rigidly anchored to the base or cylinder section 57 ofthe second three section ram 29. Both of the rams 28 and 29 arepreferably constructed in the manner disclosed in prior copendingapplication Ser. No. 76,373, filed Sept. 28, 1970, for MULTl-SECTIONHYDRAULIC RAM, now Pat. No. 3,696,712, issued Oct. 10, 1972. The supportplates 55 form a rest for the forward extremity of the rod section 32 onthe cylinder section 57 but limited vertical movement between theelements 32 and 57 is allowed due to the slots 56. The plates 55 formthe only direct connection between the two hydraulic rams 28 and 29which are otherwise independently suspended or supported within thetelescopic boom.

The ram 29 is disposed beneath the ram 28 with the cylinder section 57directly below the rod section 32, FIG. 2, when the boom is fullyextended. The rear end of cylinder section 57 is pivotally secured at 58to the inner end of the second mid-section 23 of the boom. As shown inFIG. 11, this pivotal connection comprises trunnions on the cylindersection 57 pivotally supported within bearings 59, rigidly secured tothe vertical side walls of the second mid-section 23.

Referring to FIGS. 3B and 9, the cylinder section 57 is furthersupported by a wiper bearing 60 which engages slidably over the cylindersection 57 and has its base 61 fixedly secured to the bottom wall of thethird mid-section 24. Another housing 62 formed of rod stock andincluding only two truss-like side webs 62, FIG. 9, is disposed belowthe housing 50 and has its rear end rigidly secured to a vertical plate64 spanning the rear end of third mid-section 24 and rigid therewith.This plate 64 has an opening receiving the cylinder section 57, FIG. 10.The top and bottom sides of the housing 62 are left open as shown inFIG. 9 and this allows the truss-like housing to clear the plates 55which are fixed to the top of cylinder section 57 during retraction ofthe boom, FIG. 4.

The mid-section 65 of ram 29 has its leading end secured rigidly to ablock 66 and the forward end of housing 62 is also rigidly secured tothis block through the corner rods 67 of the two housing sides.Referring to FIGS. 6, 7 and 8, the block 66 is supported floatingly in apair of opposing vertical guide channels 68 by the action of acompressible spring 69 upon which the block 66 is seated. The spring, inturn, rests upon a fixed plate 70 or bracket secured to a skid base 71integral with the two guide channels 68. The skid base 71 slides on thebotton wall of the extensible and retractable boom fly section 25. A pinextension 72 dependingly rigidly secured to the block 66. projectsthrough the bore of spring 69 and carries a head 73 below the fixedplate 70 to limit upward displacement of the block. The plate or bracket70 also has a transverse elongated slot 74 therein, FIG. 8, to allowsome lateral displacement of the block and the mid-section 65 of the ram29 to which it is attached. Therefore, the leading end of the rammid-section 65 is floatingly supported resiliently in the verticaldirection by the spring and guide means and can have limited lateralmovement. Extension of the ram mid-section 65 will pull the boommid-section 24 forwardly becausethe housing 62 has its rear endconnected with the plate 64 on the midsection 24.

In some cases, the wiper bearing 60, FIG. 9, may be spring-mounted likethe block 66. In such cases, guide channels, like the channels 68, willbe fixed to boom mid-section 24 near its rear end. With properclearances, however, the mounting shown in FIG. 9 is sufficlent.

The ram 29 has a leading rod section 75 extending to substantially theforward end of fly section 25 and car-' rying a cross pin 76 similartothe pin 54 of rod section 32. The pin 76 engages slidably withinvertical slots 77 of upstanding anchoring plates 78 having their lowerends fixedly secured to the bottom wall of the boom fly section. Thisarrangement allows the forward end of rod section 75 to have limitedvertical movement relative to the fly section 25, and as evidenced bythe lengths of the slots 77, the extent of this movement is I greaterthan the possible movement of the rod section 32 allowed by the shorterslots 56. The plates 78 stabilize the rod sections 75 against lateralmovement in the same manner that the plates 55 act on the rod section 32of the ram 28. i 1

'Referring to diagrammatic FIG. 14, there is illustrated withconsiderable exaggeration how the mounting of the two three-section rams28 and 29 within the telescopic boom in the described manner allowsthese rams to remain substantially straight and thus free of leakagedespite the inherent cocking and some bending of the several boomsections, particularly when the boom is fully extended. Even though thiscocking and bending is considerable in practice as emphasized by thediagram, the two hydraulic rams are allowed to remain relatively free ofbending stress normal to their axes because of their independentmountings and their resilient and lost motion supporting points,abovedescribed.

In the operation of the five section boom, the rams 28 and 29 shouldnormally be operated in sequence. That is to say, if only a limited boomlength is required, the ram 28 is actuated so that the boom sections 24and 25 will remain fully retracted. This results in a much stronger boomthan would be the case were the ram 29 extended first.

In FIG. 15, there is shown a modified form of wiper bearing having alimited universal adjustment or movement, and in some cases thisstructure may be employed in lieu' of the spring-suspended wiper ring34in FIG. 13 and the similar suspension means for the housing 39 shownin FIG. 11. In FIG. 15, the wiper bearing element which would receivethe ram base section is indicated by the numeral 79, and this element isspherically formed externally for universal swiveled movement within acarrier block 80 having a spherically curved recess 81. The block 80 isspring-mounted above and below by suitable springs 82 and 83 seatedwithin recesses 84 of a cage 85 attached fixedly to the firstmid-section 22 of the boom in lieu of the bracket 38. In terms of thismodification, the mounting for the particular ram provides for limitedmovement within the boom in all directions or universally, in additionto resilient support primarily in a vertical direction This structure isalso adaptable for use in lieu of floating block 66, FIG. 6, or wiperbearing 60, FIG. 9. In the use of this modification for floating block66, rods 67 and ram mid-section 65 are connected to spherical element79.

It may now be seen that the invention solves successfully the principalproblems which have retarded the manufacturing and using of a fivesection hydraulically operated telescopic crane boom. By means of theinvention, the two three-section hydraulic rams and their 'requiredhousings which connect them back to the rear ends of certain boomsections have all been successfully mounted within the interior of theboom. Each extensible section of each ram is positively connected withone of the four extensible boom sections so that the boom is fullypowered. Additionally two rams are separately mounted so that anystresses developed by the extension of one will not be transmitted tothe other. Each ram is resiliently supported at critical points or issupported through lost motion connections with the adjacent boomsections so that the inevitable cocking and bending of the boom will notbe reflected by bending and misalignment of the rams. Serious leakage ofthe rams is-thus avoided.

The terms and expressions which have been employed herein are used asterms of description and not of limitations, and there is in intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described or portions thereof but it isrecognized that various modifications are possible within the scope ofthe invention claimed.

I claim:

1. A fluid pressure actuated extensible boom comprising pluraltelescopically interfitting extensible and retractable boom sectionsincluding a base section, a mid-section, and at least one furthersection, fluid pressure operated telescoping ram means extendinglongitudinally within said boom sections and operable to extend andretract such sections, said ram means com prising at least athree-section double telescoping ram having a base section, amid-section and a rod section of successively decreasing diameters, thebase section of the ram connected to the base section of the boom, ahousing on the mid-section of the ram secured to the leading end of theram mid-section and having its rear end secured to the rear of said boommid-section said further section adapted to telescope over said housing,the rod section of said ram connected to said further section of theboom, and resiliently yielding intermediate suspension means for the ramwithin the boom sections comprising a first resiliently yieldingsuspension unit connected adjacent the rear end of said boom midsectionand being slidably engaged on the outside surface of the ram basesection and a second resiliently yielding suspension unit connectedadjacent the rear of said further boom and being in slidable supportingengagement with the outside of said housing.

2. In a crane boom, plural telescopically interfitting extensible andretractable boom sections including a base section, first, second andthird mid-sections and a fly section, first and second three sectiondouble telescoping rams within the boom sections operable to extend andretract such sections, each of said rams having a base section, amid-section and a rod section, the base section of the first ram securedto the boom base section and the base section of the second ram securedto the second mid-section of the boom, first and second housings on themid-section and rod section of the first ram having their rear endssecured respectively to the first and second boom mid-sections, thesecond housing adapted to telescope over the first housing, a thirdhousing on the mid-section of the second ram having its rear endconnected to the rear end of the third midsection of the boom, saidfirst, second and third housings formed of rods in the form of a latticestructure, the rod section of the second ram having a connection withthe fly section of the boom, and yielding suspension means for the ramswithin the boom sections comprising plural suspension units for thefirst and second rams having connections with plural sections of theboom, whereby the rams are relieved of stresses caused by cocking andbending of the boom sections.

3. The structure of claim 2, and at least the first and second housingsbeing of box-like formation in cross section.

4. The structure of claim 2, and said rams in all operating positionsarranged at least partly in side-by-side overlapping relationship, and alateral member on one ram having a lost motion connection with a sectionof the other ram.

5. The structure of claim-2, wherein one of said suspension unitscomprises a resilient support on the midsection of one of said ramsincluding a shoe element having sliding engagement with the fly sectionof the boom.

6. In a crane boom, plural telescopically interfitting extensible andretractable boom sections including a base section, first and secondmid-sections, and at least one further section, fluid pressure operatedtelescoping ram means within the boom sections operable to extend andretract such sections, said ram means comprising a three-section doubletelescoping ram having a base section, a mid-section and a rod section,first and second housings on the mid-section and rod section of said ramhaving their rear ends secured respectively to the inner ends of saidfirst and second boom midsections, the second housing adapted totelescope over said first housing, said further section adapted totelescope over said first and second housings, and yielding suspensionmeans for the ram means within the boom sections, whereby the ram meansare relieved of stresses caused by cocking and bending of the boomsections.

7. The structure of claim 6, and said yielding suspen sion meansincluding plural suspension units for the ram means at spaced pointsalong the length of and intermediate the ends of the ram means, andmeans in said plural suspension units rendering said units resilientlyyielding.

8. The structure of claim 7, and said units serving to supportinglyinterconnect individual telescoping sections of the ram means with acorresponding number of boom sections.

9. The structure of claim 8, and wherein at least one of said suspensionunits includes a suspension bearing having sliding supporting engagementwith a section of the ram means.

10. The structure of claim 9, and wherein said suspension unit furthercomprises a spring suspension means for said bearing having a connectionwith an adjacent section of said boom.

11. A crane boom as set forth in claim 6 in which said yieldingsuspension means for the ram means includes plural suspension units forthe three section ram including a first unit on the first mid-section ofthe boom having sliding supportive engagement with the base section ofthe three section ram, and a second unit on the second mid-section ofthe boom having sliding supportive engagement with said first housing.

12. A crane boom as set forth in claim 6 in which said yieldingsuspension means includes plural mounting units which interconnectsections of the ram means with adjacent sections of the boom.

13. The structure of claim 12, and at least one of said mounting unitsfor said ram including a bearing member supporting a section of the ramand a spring support for the bearing member having a connection with anadjacent section of the boom.

14. The structure of claim 12, and wherein at least one of saidsuspension units includes a bearing having sliding supporting engagementwith a section of the ram means, and a carrier for said bearing allowingthe bearing to swivel universally.

15. The structure of claim 14, and a spring mounting for said carrier.

16. The structure of claim 6, wherein said yielding suspension meanscomprises plural suspension units for said ram having connections withplural sections of the boom.

1. A fluid pressure actuated extensible boom comprising pluraltelescopically interfitting extensible and retractable boom sectionsincluding a base section, a mid-section, and at least one furthersection, fluid pressure operated telescoping ram means extendinglongitudinally within said boom sections and operable to extend andretract such sections, said ram means comprising at least athree-section double telescoping ram having a base section, amid-section and a rod section of successively decreasing diameters, thebase section of the ram connected to the base section of the boom, ahousing on the mid-section of the ram secured to the leading end of theram mid-section and having its rear end secured to the rear of said boommid-section said further section adapted to telescope over said housing,the rod section of said ram connected to said further section of theboom, and resiliently yielding intermediate suspension means for the ramwithin the boom sections comprising a first resiliently yieldingsuspension unit connected adjacent the rear end of said boom mid-sectionand being slidably engaged on the outside surface of the ram basesection and a second resiliently yielding suspension unit connectedadjacent the rear of said further boom and being in slidable supportingengagement with the outside of said housing.
 2. In a crane boom, pluraltelescopically interfitting extensible and retractable boom sectionsincluding a base section, first, second and third mid-sections and a flysection, first and second three section double telescoping rams withinthe boom sections operable to extend and retract such sections, each ofsaid rams having a base section, a mid-section and a rod section, thebase section of the first ram secured to the boom base section and thebase section of the second ram secured to the second mid-section of theboom, first and second housings on the mid-section and rod section ofthe first ram having their rear ends secured respectively to the firstand second boom mid-sections, the second housing adapted to telescopeover the first housing, a third housing on the mid-section of the secondram having its rear end connected to the rear end of the thirdmid-section of the boom, said first, second and third housings formed ofrods in the form of a lattice structure, the rod section of the secondram having a connection with the fly section of the boom, and yieldingsuspension means for the rams within the boom sections comprising pluralsuspension units for the first and second rams having connections withplural sections of the boom, whereby the rams are relieved of stressescaused by cocking and bending of the boom sections.
 3. The structure ofclaim 2, and at least the first and second housings being of box-likeformation in cross section.
 4. The structure of claim 2, and said ramsin all operating positions arranged at least partly in side-by-sideoverlapping relationship, and a lateral member on one ram having a lostmotion connection with a section of the other ram.
 5. The structure ofclaim 2, wherein one of said suspension units comprises a resilientsupport on the mid-section of one of said rams including a shoe elementhaving sliding engagement with the fly section of the boom.
 6. In acrane boom, plural telescopically interfitting extensible andretractable boom sections including a base section, first and secondmid-sections, and at least one further section, fluid pressure operatedtelescoping ram means within the boom sections operable to extend andretract such sections, said ram means comprising a three-section doubletelescoping ram having a base section, a mid-section and a rod section,first and second housings on the mid-section and rod section of said ramhaving their rear ends secured respectively to the inner ends of saidfirst and second boom mid-sections, the second hoUsing adapted totelescope over said first housing, said further section adapted totelescope over said first and second housings, and yielding suspensionmeans for the ram means within the boom sections, whereby the ram meansare relieved of stresses caused by cocking and bending of the boomsections.
 7. The structure of claim 6, and said yielding suspensionmeans including plural suspension units for the ram means at spacedpoints along the length of and intermediate the ends of the ram means,and means in said plural suspension units rendering said unitsresiliently yielding.
 8. The structure of claim 7, and said unitsserving to supportingly interconnect individual telescoping sections ofthe ram means with a corresponding number of boom sections.
 9. Thestructure of claim 8, and wherein at least one of said suspension unitsincludes a suspension bearing having sliding supporting engagement witha section of the ram means.
 10. The structure of claim 9, and whereinsaid suspension unit further comprises a spring suspension means forsaid bearing having a connection with an adjacent section of said boom.11. A crane boom as set forth in claim 6 in which said yieldingsuspension means for the ram means includes plural suspension units forthe three section ram including a first unit on the first mid-section ofthe boom having sliding supportive engagement with the base section ofthe three section ram, and a second unit on the second mid-section ofthe boom having sliding supportive engagement with said first housing.12. A crane boom as set forth in claim 6 in which said yieldingsuspension means includes plural mounting units which interconnectsections of the ram means with adjacent sections of the boom.
 13. Thestructure of claim 12, and at least one of said mounting units for saidram including a bearing member supporting a section of the ram and aspring support for the bearing member having a connection with anadjacent section of the boom.
 14. The structure of claim 12, and whereinat least one of said suspension units includes a bearing having slidingsupporting engagement with a section of the ram means, and a carrier forsaid bearing allowing the bearing to swivel universally.
 15. Thestructure of claim 14, and a spring mounting for said carrier.
 16. Thestructure of claim 6, wherein said yielding suspension means comprisesplural suspension units for said ram having connections with pluralsections of the boom.